A various types of optical devices allowing a viewer to perceive a virtual image superimposed on an image in real space have been recently developed. An example of such optical devices includes a wearable optical device, and in particular, a device that is worn by the user on the head is known as a head-mounted display (HMD). An exemplary type of the HMD is known in which a half mirror serving as a display surface is provided in front of the viewer's pupils and an image (real image) is formed on the display surface. Another type of the HMD is developed in which guidance of image display light to the viewer's pupils using an optical system allows the viewer to perceive an image (virtual image). As one example, Patent Literature 1 discloses the technique that implements an HMD capable of guiding the image display light in the lateral direction with respect to the viewer's pupils to be incident on the viewer's pupils.
For example, the use of the technique disclosed in Patent Literature 1 or other techniques becomes increasingly reducing in size and weight of the wearable optical device such as HMD. The continuous long-term use without frequent charging or the like is desirable due to the characteristics of wearable devices. Under such circumstances, various techniques for reduction in power consumption of the wearable optical device have been developed. As one example, Patent Literature 2 discloses a technique for reduction in power consumption of an HMD by shutting off the power when a sensor for detecting a movement determines that the HMD is not mounted and then by supplying again the power when any movement is detected.